This invention relates to a construction material including a concrete body and a metallic material and adapted for preventing or minimizing chemical corrosion of metal pipes extending therefrom and a method of producing same. The present invention is also directed to a method of preventing such chemical corrosion.
It is known that iron pipes such as city gas pipes in soil or water are corroded when such pipes are electrically contacted with reinforced concrete of buildings. Such corrosion, which is termed macrocell corrosion, is considered to result from the creation of a difference in electrical potential between the reinforcing bars of the reinforced concrete and the gas pipes, which is caused by a difference in hydrogen-ion concentration between the concrete body within which the reinforcing bars are embedded and the soil or water in which the gas pipes are present.
FIG. 3 of the accompanying drawings schematically illustrates the above macrocell corrosion phenomenon. The reference numeral 1 denotes a concrete wall within which reinforcing bars 6 are embedded. A gas pipe 2 extends through the wall 1 into soil 3. Since the alkalinity of the concrete wall 1 is higher than that of the soil 3, the electrical potential of the reinforced bars 6 is higher than that of the gas pipe 3, so that a macrocell current flows as shown by the arrow 5. Corrosion of the gas pipe 2 occurs at a portion 4 from which the current flows into the soil 3. Such a macrocell current is generated even when the gas pipe 2 is not directly contacted with the reinforcing bars 6.
One known method for the prevention of the corrosion of pipes due to such a macrocell current is illustrated in FIG. 4, in which the same reference numerals as those in FIG. 3 designate similar component parts. In this method, that portion of the gas pipe 2 which is located in the soil 3 is surrounded by an insulating layer 8 such as a polyethylene resin coating to prevent a current from flowing from the pipe 2 to the soil 3. Also, a bore 7 is formed in the concrete wall 1 to prevent the pipe 2 from electrically contacting with the concrete wall 1 and with the reinforcing bars 6.
This method is not fully satisfactory from the standpoint of economy because it is troublesome to form the bores 7 in the wall 1 and to provide the insulating layer around the pipes 2. Further, when the insulating layer 8 is injured for some reasons, a macrocell current, if generated, will concentrically flow at the injured portion so that the corresponding portion of the gas pipe 2 is more susceptible to corrosion.
It is known to incorporate a nitrite into a concrete body so as to prevent the corrosion of the reinforcing bars embedded therewithin. This technique is useless in preventing the occurrence of macrocell current, i.e. in preventing the corrosion of gas pipes extending from the concrete body.